mach-msm: msm-pm: fix warning

arch/arm/mach-msm/msm-pm.c: In function ‘msm_pc_debug_counters_copy’:
arch/arm/mach-msm/msm-pm.c:814:17: warning: iteration 3u invokes
undefined behavior [-Waggressive-loop-optimizations]
error, forbidden warning: msm-pm.c:814
scripts/Makefile.build:308: recipe for target 'arch/arm/mach-msm/msm-
pm.o' failed
make[1]: *** [arch/arm/mach-msm/msm-pm.o] Error 1
Makefile:806: recipe for target 'arch/arm/mach-msm' failed